Reports have implicated aged spermatozoa with an increased frequency of chromosomally abnormal blastocysts and fetal abnormalities in the rabbit, and as a teratogenic factor in humans. There has been no experimental investigation to determine the specific effect of sperm age on the frequency of chromosome anomalies. The experiments in this proposal are designed to provide not only an understanding of the role of the aging sperm in the induction of chromosome anomalies but also the mechanisms by which the anomalies may arise. Herein is proposed a developmental and karyological analysis of a) first cleavage metaphases, b) pre- and c) post-implantation conceptuses resulting from mouse oocytes fertilized by sperm aged for different periods in each of the following: 1) the male tract following surgical ligation of the corpus epididymis, 2) in the female tract by varying the time of insemination relative to ovulation and 3) in vitro after storage at temperatures above and below freezing. Structural chromosome rearrangements will be detected by banding techniques. This new approach of studying first cleavage metaphase provides the advantage of detecting whether or not chromosome anomalies in a conceptus are transmitted by the aged male gamete or indirectly by the female gamete. Furthermore, fertilization errors may be detected. The DNA replication pattern in first cleavage arrests and the onset of RNA synthesis in embryos resulting from aged sperm will also be studied. Morphological studies of early cleavage and sperm-ovum contact of oocytes fertilized by aged sperm will be evaluated by light microscopy in ova collected a) from the ampulla in the periovulatory period and b) after in vitro fertilization. Sperm numbers at the fertilization site and in the oviduct during ovulation will be compared in experimentals and controls. Differences in the number of abnormal zygotes and embryos from controls and experimentals as well as differences in sex ratio will be treated with a chi square analysis.